Sorry Elizabeth, I failed to mention a specific page as an example. 
Using Source Citation: Year: 1850; Census Place:  , Campbell, Virginia;
Roll: M432_938; Page: 183; Image: 366, from Ancestry.com. See dwelling 819
and 821 for a typical example of the use on the 1 in parentheses. In
dwelling 821 with John Davis as the head of household, the 2nd person is the
widowed sister, #3 is unknown but likely his sister-in-law, next are four
Callaham women and two have a 1 beside their name. Last is the brother of
the head of household. 
Also using Source Citation: Year: 1850; Census Place:  , Campbell, Virginia;
Roll: M432_938; Page: 183; Image: 365; see dwelling #815 for Thomas Cock,
where two children have the 1 beside their name. 

Actually if you are using Ancestry.com to view these images you can page
forward or backward and see this occurring quite often.
My guess is that this is some indication of their relationship, as born of
the 1st wife maybe. Thanks for your time and effort.

Regards,
Don Trent in Texas
My Family History research is now located at:
http://wc.rootsweb.com/cgi-bin/igm.cgi?db=ht1642&I11.x=0&I11.y=0 
and: http://dtpm64.googlepages.com/home For information on the Trent surname
Y-DNA project visit:
http://www.familytreedna.com/public/Trent%20Y-DNA%20Project/  

To subscribe, change options, or unsubscribe, please see the instructions at
http://listlva.lib.va.us/archives/va-roots.html